Proposal (350) to South American Classification Committee

 

Incluir Xolmis salinarum dentro de X. rubetra

 

Nores e Yzurieta (1979) describieron esta nueva taxa como una subespecie de X. rubetra basados en caracteres morfológicos, especialmente coloración, y comportamiento. Este taxa tiene un patrón de colores similar a X. rubetra pero con bastante más blanco. Además es bastante más chica y no tiene rayas en el pecho (ver foto adjunta). Ambas especies son gregarias y terrícolas, pero salinarum parece aún más adaptada a hábitos terrícolas y corre por el suelo a la manera de un playero (plover).

 

Hasta 1987 fue considerada como una subespecie, pero en ese aĖo, Narosky e Yzurieta (Guía para la identificación de las aves de Argentina y Uruguay) la elevan a especie. De allí en adelante, se la ha considerado indistintamente como subespecie (por ejemplo Stotz et al. Neotropical Birds, Nores 1996: Avifauna de la Provincia de Córdoba) o especie (Ridgely and Tudor: Birds of South America, y en el HBW).

 

La vegetación de las salinas Grandes y de Ambargasta, donde habita X. salinarum es en algunos aspectos similar ecológicamente a la estepa patagónica. Por esta razón, varias especies patagónicas, durante su migración, pasan el invierno en las salinas o tienen poblaciones ya establecidas allí; por ejemplo: Leptasthenura aegithaloides, Asthenes pyrrholeuca, Agriornis microptera, Agriornis murina, Anairetes flavirostris, Mimus patagonicus y Phrygilus carbonarius.

 

Xolmis rubetra nidifica en el sur de Argentina y migra en otoĖo a las provincias centrales. Evidentemente, X. salinarum deriva de una población de X. rubetra que se estableció en las salinas. El asunto ahora es determinar si salinarum es una subespecie muy diferente (megasubespecie) de rubetra o ya ha alcanzado el status de especie.

 

Literatura citada:

Nores, M., e Yzurieta, D. 1979. Una nueva especie y dos nuevas subespecies de Aves (Passeriformes). Acad. Nac. Cienc. Cba. Misc. No. 61.

 

Manuel Nores, May 2008

 

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Comments from Remsen: "YES. The reason we currently rank salinarum as a species is largely an accident. The original draft of Dickinson (2003) started out as treating salinarum as a species, and that was the one we followed, but by the time the draft went to press, we had demoted it to subspecies rank given the lack of evidence for deviating from Manuel's original designation. Therefore, if we were strictly using the published version of Dickinson (2003), we would treat salinarum as a subspecies and any proposal would have to provide evidence for species rank. Not only will a vote yes to correct a change that did not arrive in time, but also looking at the evidence for species rank ... well there is none. The voice (a good barometer for species rank in Tyrannidae), for example, is unknown according to HBW account. Finally, the original discoverer considered it an isolated, well-marked population of rubetra, and I see no reason to change from his original or current assessment."

 

Comments from Cadena: "YES. Manuel's first-hand experience with the birds and Van's comments convince me that this is the best course of action."

 

Comments from Stiles: "YES. I agree with Van's comments, we need more evidence before contradicting Manuel's judgment on this point - he surely has more first-hand experience with this taxon, and the original split was not based upon anything like new evidence."

 

Comments from Stotz: "YES. I can see no evidence to support treating this taxon as a distinct species."

 

Additional comments by Mark Pearman, Nacho Areta and Hernán CasaĖas:

Much new data has been acquired in terms of the basic biology for X. [r.] salinarum since its type description, yet little has been advanced with the comparative biology of the more widespread X. (r.) rubetra, since salinarum has acted like a magnet to ornithologists and birders alike because of its rarity and restricted range (e.g. Aspiroz 2006). Most of the comparative data, for the two taxa is either old or historical, but is nevertheless pertinent to the taxonomy in question; some of it is included in the type description and some not. Here we add a summary of the distinctions between the two taxa from published data (to source), and also note that the general consensus in the literature is rather different from the stated two publications in favour of subspecies status versus three against (in #350) after finding another nine books which treat salinarum at species rank (Olrog 1984, Canevari et al. 1991, Chebez 1994, Collar et al. 1994, Stattersfield et al. 1998, Straneck & Carrizo 1991, Mazar Barnett & Pearman 2001, Di Giacomo 2005, Veiga et al. 2005). Moreover, we note that it was Claes Christian Olrog (see Olrog 1979) who first questioned the subspecific status of salinarum using the determination X (r.) salinarum and later elevated it to species rank (Olrog 1984) well before Narosky & Yzurieta (1987) did so, as indicated in proposal #350. It is also noteworthy that in their type description Nores and Yzurieta (1979) wrote "Diagnostico: esta raza, perfectamente caracterizada, difiere notablemente de la tipica a tal punto que podria ser considerada una especie distinta."

 

Plumage distinctions (Sources: Nores & Yzurieta 1979, Aspiroz 2006, photographs, field observations)

 

a) Supercilium:- Bold and white in rubetra. In salinarum, it typically joins across the nape forming a diadem. 

b) Nuchal band: - broad and white (in addition to the diadem) in salinarum, but lacking altogether in rubetra, thus salinarum shows two white bands crossing the nape.

c) Back (mantle): - brown in salinarum, contrasting with its rusty crown, but rusty in rubetra and concolorous with its crown.

d) Lesser and median upperwing-coverts: - pure white in salinarum thus exhibiting great contrast with the back, and rusty brown with white tips to the median wing-coverts (when fresh) in rubetra,

e) Lower rump and uppertail-coverts: - pure white in salinarum and thus very striking in flight, but brown with fine whitish fringes to the uppertail-coverts (if one looks closely) rubetra and thus showing no particular contrast.

e) Lower rump and uppertail-coverts: - pure white in salinarum and thus very striking in flight, but brown with fine whitish fringes to the uppertail-coverts (if one looks closely) rubetra and thus showing no particular contrast.

f) Breast streaking: - none or fine, indistinct short streaks restricted to the sides of the breast, rarely forming a narrow pectoral band in salinarum, but heavily streaked over the entire breast in rubetra.

g) Malar region and ear-coverts: - a fine isolated black malar at best, or with a few additional sparse black streaks in this region in salinarum, compared to ear-coverts and malar region entirely and notably streaked black in rubetra.

 

- Arguments in favour of species rank. Subspecies described for X. irupero, X. pyrope and X. cinerea have all been questioned at one time or another, are barely diagnosable (Farnsworth & Langham 2004), and have invariably been accepted by one author only to be discarded by another. Other members of the genus such as X. coronatus and X. velatus have always been considered monotypic. Plumage differences between rubetra and salinarum therefore come as a huge surprise within the genus Xolmis as a whole (see Vuilleumier 1971, 1994) and are striking both in the field and among specimens.

 

To view single photographs of rubetra and salinarum enter http://picasaweb.google.es/XRubetraSalinarum and click on "Proyección de diapositivas". More photographs of salinarum and a host of other Xolmis, Agriornis and Muscisaxicola can be also found at http://www.avespampa.com.ar/Tyrannidae.htm.

 

Wing-raising displays described for the genus, suggest that the strikingly white wing pattern of salinarum might play a role in reproductive isolation with rubetra. Vuilleumier (1994) noted that in many species of bush and ground tyrants in the genera Myiotheretes, Xolmis, Neoxolmis, Agriornis, and Muscisaxicola, reproductive isolation between closely related species may be correlated with size or body mass and/or color patterns, although conceivably both size and color pattern differences could be enhanced during some of the vocal and/or non-vocal displays.

 

- Arguments against species rank. None. Nores (in proposal #350) suggested that salinarum could be a "megasubspecies". We are not familiar with this term, and it certainly is not attached to any meaningful Linnean taxonomic category. Moreover, this statement does not specify which elements would be critical to support specific, subspecific or "mega-sub-specific" status for salinarum.

 

Size (Sources: Nores & Yzurieta 1979, museum specimens) All authors agree that salinarum is smaller than rubetra, and a table of standard measurements was provided by Nores & Yzurieta (1979) but only for the holotype. These authors only compared the wing chord of salinarum (106 mm.) with rubetra (127 mm.). Additional data, although perhaps arbitrary and with only a small sample for salinarum, are total length measurements taken at the time of collection, presented on specimen tags as follows:

 

rubetra:- 20.83 Ī 1.63 cm. (n = 18, IADIZA, MACN)

salinarum- 18.25 Ī 0.75 cm. (n = 2, MACN, FML)

 

These data indicate that salinarum is almost 12% shorter than rubetra.

 

- Arguments in favour of species rank. No such difference in size exists between any described Xolmis subspecies and its nominate form. See above for possible role of size in species recognition.

 

- Arguments against species rank. None.

 

Migratory status (Sources: Nores & Yzurieta 1979, Olrog 1979, Di Giacomo 2005, De Lucca & Saggese 1992, Vuilleumier 1994)

 

rubetra:- An austral migrant breeding in the lowlands, plateaus and Andean foothills from s. Mendoza, Neuquén, Río Negro, La Pampa and s. Buenos Aires south to Chubut with one record of a pair from nc. Santa Cruz, and winters north to Tucumán, se. Santiago del Estero, w. Chaco (unpublished), n. Santa Fe and Entre Ríos.

 

salinarum: - Resident with very local movements at the Salinas Grandes, nw. Córdoba-se. Catamarca and the Salinas de Ambargasta, sw. Santiago de Estero. Recent records of groups of 4-10 in and around PN Sierra de Las Quijadas, nw. San Luis suggest another local breeding population.

 

- Arguments in favour of species rank. Although we acknowledge the existence of polymorphism in migratory behaviour in Muscisaxicola (Chesser 2000), the divergent migratory patterns of rubetra and salinarum are unknown within any other Xolmis species.

 

- Arguments against species rank. None.

 

Sociality (Sources: Serié 1923, Cobos & Miatello 2001)

 

rubetra- The largest flock on record was a report of 1000 individuals, and large winter flocks seem to be regular prior to migration and when reaching wintering grounds before dispersal.

 

salinarum- The largest flocks on record are 30 to 65 individuals, although this is unusual and the species is normally found in small groups in winter of just a few individuals or rarely up to 15 (HC pers. obs.). These are roving flocks as opposed to migratory flocks.

 

- Arguments in favour of species rank. The distinct social aggregation patterns of rubetra and salinarum are unknown within any other Xolmis species.

 

- Arguments against species rank. None.

 

Habitat (Sources: Vuilleumier 1994, Farnsworth & Langham 2004, Di Giacomo 2005)

 

rubetra- Arid Patagonian shrubsteppe in areas with scattered bushes e.g. Larrea, Schinus, Baccharis, Chuquiraga and Condalia), often in adjacent Salicornia beds on salt-impregnated soil; and Patagonian grass-steppe especially with Festuca bunch-grass with or without low shrubs; also in rather tall dense Monte desert woodlands. Frequently close to water. In winter recorded on ploughed fields and Stipa grasslands. Passage migrants may occur in unusual habitats such as reed and Schoenoplectus sedgebeds, and even in soya crops (HC per. obs.).

 

salinarum- Restricted to the borders of open salt flats often close to saline water courses or standing water; specifically, in areas with a Salicornia mat covering the salt-impregnated soil or in isolated groups of thorn bush (Atriplex, Heterostachys, Prosopis reptans and Cyclolepis genistoides); less commonly at the edge of chaco woodlands bordering the salt flats. Note that this is a very restricted microhabitat from which the species never strays far.

 

- Arguments in favour of species rank. Rubetra shows a great deal of plasticity towards its breeding and wintering habitat, whereas the only habitat of salinarum is very specific, highly restricted, and different from that of rubetra. Since rubetra is highly vagile, its absence from the salinas during the breeding season (and probably also during the winter) suggests that it avoids this habitat, which would, in turn, suggest that salinarum is reproductively isolated.

 

- Arguments against species rank. None.

 

Nestlings (Sources: Vuilleumier 1994, Cobos & Miatello 2001)

 

rubetra- Covered with brownish gray down, orange gape.

salinarum- Covered in pearl-grey down. Yellowish bill with whitish commisure and pink tarsus.

 

- Arguments in favour of species rank. Both descriptions are first hand and relatively recent, but do not coincide.

 

- Arguments against species rank. None.

 

Vocalizations. There is little material on the vocalizations of rubetra and salinarum, a lack which seems to be symptomatic of the ground-tyrants, which seldom sing and hence are seldom recorded. Vocalizations have never played a key role in the taxonomy of the ground-tyrants, and most taxonomically valuable information seems to be morphological, distributional and ecological (Vuilleumier 1994). Hence, we see no reason to treat the lack of evidence on the vocalizations as an impediment to progress in the taxonomy of rubetra and salinarum.

 

Legality of taxonomic changeSalinarum was described as a subspecies of X. rubetra based on an initial subjective judgment about its distinctiveness. However, whether it can be arbitrarily elevated to species rank is a valid question. One answer is that it already has been elevated (e.g., Olrog 1984, Ridgely & Tudor 1994), and this change has been followed by the vast majority of authors (see first paragraph of this comments). If this rank elevation was not possible, we would not have written these comments and would not be arguing the point with SACC today. 

 

Final comment. In sum, available published evidence clearly shows that rubetra and salinarum differ dramatically in both ecology and morphology, and there is no evidence of intergradation or genetic contact between these taxa. Our own extensive field experience with both taxa is in full agreement with the published evidence. We propose a NO vote for proposal #350. Voting for NO would keep salinarum as a valid species, recognising the species-level differences with other Xolmis based on published evidence, and in agreement with a widely adopted taxonomy.

 

New references (not cited in SACC main reference list):

Azpiroz, A. (2006) Photospot: Salinas Monjita Xolmis salinarum. Neotropical Birding 1: 78-80.

Cobos, V. & Miatello, R. (2001) Descripción del nido, huevo y pichón de la Monjita Salinera (Neoxolmis salinarum). Hornero 16(1): 47-48.

Collar, N.J., Crosby, M.J. & Stattersfield, A.J. (1994) Birds to Watch 2The World List of Threatened Birds. BirdLife Conserv. Series No.4. BirdLife Internat., Cambridge, U.K.

De Lucca, E.R. & Saggese, M.D. (1992) Aves del Departamento Deseado, Santa Cruz. Hornero 13(3): 259-260.

Di Giacomo, A.S. ed. (2005) Áreas de importancia para la conservación de las aves en Argentina. Sitios prioritarios para la conservación de la biodiversidad. Temas de Naturaleza y Conservación 5. Aves Argentinas/Asociación Ornitológica del Plata, Buenos Aires.

Farnsworth, A. & Langham, G.M. (2004) Genus Xolmis in: del Hoyo et al. eds. (2004) Handbook of the Birds of the World. Vol. 9. Lynx Edicions, Barcelona.

Olrog, C.C. (1984) Las Aves Argentinas: Una Nueva Guía de Campo. A.P.N., Buenos Aires. Serié, P. (1923) Miscelanea Ornitología. Hornero 3(2): 189-191.

Stattersfield, A.J., Crosby, M.J., Long, A.J. & Wege, D.C. (1998) Endemic Bird Areas of the World: Priorities for Biodiversity Conservation. BirdLife Conservation Series No.7, Cambridge, U.K. 

Straneck, R & Carrizo, G. (1991) Lista de Campo para las Aves Argentinas. L.O.L.A., Buenos Aires.

Vuilleumier, F. (1994) Nesting, behaviour, distribution, and speciation of Patagonian and Andean ground tyrants (Myiotheretes, Xolmis, Neoxolmis, Agriornis, and Muscisaxicola). Ornitologia Neotropical 5: 1-55.

 

Additional comments from Remsen: "In view of the excellent summary above, particularly with respect to comparisons to other Xolmis, I change my vote to NO."

 

Additional comments from Nores: "Los comentarios de Pearman, Areta y CasaĖas resultan sorprendente, ya que raramente se da una situación así. O sea que el que describió el ave propone bajarle el status taxonómico, mientras que los críticos tratan de buscar todos los elementos posibles para elevar su status. Siempre es al revés. Aunque a mí personalmente me conviene que mi propuesta sea rechazada y salinarum sea considerada especie, ya que soy uno de los que la describió, no he querido influenciar en la propuesta al resto del comité buscando minuciosamente las diferencias ni tampoco los trabajos que la citan como especie. Por esta razón, sólo mencioné que era más chica, con mucho más blanco en el plumaje y sin rayas en el pecho, y cité algunos trabajos que la consideran subespecie y otros como especie. Aunque los comentarios de Pearman, Areta y CasaĖas me parecen buenos, no me sacan la duda de que, si es una subespecie muy diferenciada o una especie, y de lo que, si estoy seguro, no se trata de dos especies que difieren dramáticamente en morfología y ecología, como seĖalan ellos. A lo sumo, levemente distintas.

 

"Estos autores también seĖalan en sus comentarios que no están familiarizados con el término "megasubespecie" y que el mismo no está adjuntado a ninguna categoría taxonómica lineana. Para una definición del término pueden ver Amadon, D. y L. L. Short. 1976. Treatment of subspecies approaching species status. Syst. Zool. 25:161-167, y una aplicación del mismo en Nores, M. 1992. Bird speciation in subtropical South America en relation to forest expansion and retraction. Auk 109:346-357."

 

Comments from Jaramillo: "NO - Well, I could not have put it better than Pearman et al. My experience with these two species confirmed to me that they were very different entities. The visual differences are actually rather well marked, and this is striking for a Tyrannid, and particularly so for a "ground tyrant relative." I mean you look at Agriornis, or Muscisaxicola and most good species (sympatric ones) often differ in elements of size, a bit on plumage tone and at most a different crown patch color. Xolmis salinarum and rubetra are visually rather distinct, when compared to other species in this group. Van worried about the lack of vocal information for this species. Well, these "ground-tyrant relatives" are notoriously quiet, and they do not seem to use voice much at all except for a few notable exceptions. Many perform aerial displays, and at least some Muscisaxicola perform the display but give no vocal accompaniment, or sometimes just a weak "chip" note repeated as the bird is in the air. Unlike most tyrants, vocalizations are not all that important in display in this group. I am sure that vocalizations would differ if you can obtain some, but they are not important in the actual species-specific displays these birds use. The fact that "flash patterns" like the wing patterns differ in Xolmis salinarum and rubetra is probably more important.

 

"I also want to underscore how unusual and specific the habitat of salinarum is, as noted by Pearman et al. In particular, how different it is from the more typical shrubby Patagonian steppe habitat used by X. rubetra. Apart from the obvious ecological differences, my guess is that salinarum probably has some physiological differences in order to deal with the high levels of salt in its habitat. Just a guess there, but it gives you a sense for how different the ecological situation is for these two species, and that does not include the resident vs. migratory nature of the two forms."

 

Additional Comments from Cadena: "For the cogent reasons presented by Pearman et al. and by Alvaro, I change my vote to NO."

 

Comments from Robbins: "NO, based on Pearman et al.'s extensive comments."

 

Additional comments from Stiles: "In view of the comments now posted, I agree that salinarum merits species status so will change my vote to NO. (It is nice to have input from people who know the birds well when I am not familiar with them!)"

 

Comments from Pacheco: "NO. Os argumentos reunidos por Pearman, Areta e CasaĖas sčo verdadeiramente suficientes para o tratamento de X. salinarum em nível de espécie."